In recent years, display devices in which input interface parts such as a touch panel and the like are mounted and in which front panels such as toughened glass decorated and printed from the viewpoint of a design property and protection of a display surface are mounted are used increasingly for liquid crystal display modules as display devices.
When a front panel such as a touch panel and the like is mounted in a liquid crystal display module, an air layer is present usually between the surface of a liquid crystal panel and a touch panel in the module, and therefore light is reflected due to an optical property in an interface between the touch panel (for example, a glass substrate) and the air layer which are different in a refractive index.
A visibility of a displayed image is notably reduced due to interfacial reflection in the above part particularly under an environment of light coming from an outside. In order to decrease a reduction in the above visibility, proposed is a technology in which a transparent optical elastomeric resin having a refractive index close to that of a glass substrate of a touch panel is filled in or bonded on an air layer part, whereby interfacial reflection is inhibited to enhance a visibility of a displayed image.
The above wholly bonding technology is called optical bonding or direct bonding, and it has come to be widely used since it has not only optical effects but also mechanical effects such as preventing a front panel from scattering and enhancing an impact resistance.
FIG. 11 is a drawing showing a display module structure of a display device in conventional technologies. As shown in the drawing, a display module 801 composed from an LCD panel 802 as a display panel comprising upper and lower substrates bonded together, a backlight unit 803 as a case for receiving the upper and lower substrates described above, a bezel 804 which is opened in a display part and incorporated into the backlight unit 803, and the like.
Also, in a liquid crystal display device equipped with a touch panel, provided, as shown in FIG. 12, a front panel 806 which is wholly bonded (optical bonding) on a display part of the display module 801 via OCR (optical clear resin: a transparent optical elastomeric resin) 805.
Further, in wholly bonding the display module 801 and the front panel 806 via the OCR 805 of a UV curing type, a dam 807 for the purpose of sealing is usually formed by the same or similar OCR in an aperture part between the bezel 804 and the LCD panel 802 at a bezel end part in order to prevent the OCR 805 from being infiltrated into the module from the aperture part between the bezel 804 and the LCD panel 802 in the display module 801.
FIG. 13 is a drawing showing a process flow of optical bonding. A dam is temporarily cured, for example, by irradiating with a UV ray of a spot type so that a coating form is not broken, while carrying out dispense coating. Then, OCR for wholly bonding is coated thereon, and the front panel and the display module are bonded together, for example, under a decompression environment. Next, the OCR is temporarily cured, for example, by irradiating with a UV ray of a spot type, and then the OCR is cured by irradiating the wholly with a prescribed dose of a UV ray by means of, for example, a conveyor UV device, whereby the OCR is cured, and the front panel and the display module are adhered.
On the other hand, the bezel part of the display module is undulated due to tolerance in forming the members and assembling them, and the bezel part and the resin dam which are to be originally adhered are separated, so that in certain cases, the dam for the purpose of sealing can not regularly be formed or is broken due to external stress exerted in bonding.
The dam described above is formed usually by coating a prescribed amount of the dam material at a fixed rate by means of a dispenser and the like, and due to tolerance in an aperture between the bezel part and the upper and lower substrates, the dam material flows and is infiltrated (this phenomenon is called sink) into a reverse side of the bezel in a large part of the aperture before temporarily curing the dam material by irradiation with a UV ray. Accordingly, the dam can not normally be formed, and an aperture is liable to be formed between the resin dam and the bezel.
If the aperture is present between the dam and the bezel in bonding, the OCR is infiltrated through the aperture into an inside of the display module. The resin infiltrated into an inside of the module is not cured even after time passes because it is not irradiated with a UV ray, and it spreads to all parts of the aperture. In the worst case, it spreads to a reverse side of the panel and an illuminated face of the backlight to cause inferior display in a certain case, and the defect that the uncured OCR leaks out from the display module is brought out in a certain case.
Alternatively, even when the bezel and the resin dam are adhered and fixed by forming normally the dam, the panel and the bezel move temporarily upward and downward respectively in a bonding step, a transporting step and the like in a certain case, which results in that adhesion between the bezel and resin dam is broken and that an infiltration route into the inside of the module is formed even if temporarily.
A method for meeting the problem of controlling protrusion (infiltration) of the OCR by forming plural dams is disclosed in Patent Literature 1 (FIG. 15).
In the above method, a display face Da adsorbed and held on a liquid crystal panel D1 in an optical display device is turned downward and faced oppositely to a bonding face Pa of a transparent tabular member P at some gap, and a first loading base 1 is moved downward to apply a pressing force onto a liquid optical resin R (OCR) with a second loading base 6.
As shown in FIG. 15, a second dam K2 is provided at an outside of a first dam K1 corresponding to a usual dam on the transparent tabular member P, and the OCR overflowing over the first dam K1 by bonding the panel D1 and the member P is blocked by the second dam K2.
Also, it is indicated that the OCR can be inhibited from overflowing by curing wholly the OCR when the overflowing OCR reaches the vicinity of the peak of the second dam K2.